1. Technical Field of the Invention
The present invention relates to a radiant heating apparatus for heat-treating one or more workpieces such as semiconductor boards or liquid crystal boards by a flash from a flash discharge lamp, and especially to a radiant heating apparatus having a discharge current detecting circuit.
2. Description of Related Art
A radiant heating apparatus that heat-treats workpieces such as semiconductor wafers by a flash light simultaneously emitted from a plurality of rod-shaped flash discharge lamps has been developed.
In a flash circuit of a conventional flash discharge lamp for a radiant heating apparatus, alternating voltage supplied from an alternating voltage power source is converted to direct current voltage by a rectifier smoothing circuit. After the direct current voltage is converted to alternating voltage via a chopper circuit by an inverter circuit, the alternating voltage is boosted by a boosting transformer and then is converted to high direct current voltage by a high voltage rectifier smoothing circuit, by which a discharge condenser is charged by the high direct current voltage. By triggering the flash discharge lamp by a trigger signal generated by a trigger circuit, the charged high direct current voltage is discharged, thereby, the flash discharge lamp emits a flash light.
However, the more the lash discharge lamp is used, the more the capacity of the condenser for such a flash circuit become lower. When the capacity of the condenser drops, then the intensity of radiation lowers, therefore, it is difficult to properly heat-treat workpieces.
In a radiant heating apparatus having a plurality of flash discharge lamps, an appropriate distance between a plurality of flash discharge lamps and workpieces is maintained. The flash discharge lamps emit a flash light simultaneously to obtain an appropriate light output, thereby, semi-conductor etc. is uniformly heated. Thus, in the radiant heating apparatus having the plurality of flash discharge lamps, if light output from one of the discharge lamps drops, the flash discharge lamps would not uniformly heat-treat the semiconductor.
In general, light output energy E is represented by E=QV/2=CV2/2 wherein the quantity of charges, the capacity of the discharge condenser, and the charged voltage of the discharge condenser is Q, C, and V respectively. A drop of light output caused by a drop of the condenser capacity is compensated by raising charged voltage V.
To raise the charged voltage V, it is necessary to know how much the capacity of the charged condenser has dropped. The capacity C may be measured by connecting a measuring device (an LCR meter etc.) to the both ends of the discharge condenser.
However, the capacity of the condenser built in the high voltage rectifier smoothing circuit is measured in addition to the capacity C. Further, in case that charges in the discharge condenser remains therein since the flash discharge lamp does not emit a flash, there is a possibility that a discharge accident occurs if the measuring device is connected to the condenser.
It is an object to measure discharge current without contacting a discharge circuit.
It is further object to compensate capacity drops of a discharge condenser.
It is still further object is to alert to an abnormal state of a discharge circuit.
The present invention provides a radiant heating apparatus for heating one or more workpieces, comprising at least one flash discharge lamp, a discharge circuit having a condenser, connected in series to the at least flash discharge lamp, for supplying voltage to the at least one flash discharge lamp, and a non-contact current detecting sensor provided in the discharge circuit wherein the current detecting sensor detects in a non-contact state discharge current flowing through the discharge circuit.
Accordingly, it is possible to detect changes of flash amount by measuring a large amount of current in a non-contact state
The radiant heating apparatus may include a power source controlling circuit wherein the power source controlling circuit controls voltage charged in the condenser based on a value detected by the non-contact current detecting sensor.
It is possible to maintain the desired flash amount by compensating changes of the flash amount caused by deterioration of the condenser whereby it is possible to uniformly heat-treat one or more workpieces by each of the flash discharge lamps.
The radiant heating apparatus may include a display circuit wherein the display circuit alerts to an abnormal state of the discharge circuit based on a value detected by the no-contact current detecting sensor.
Therefore, it is possible to alert to an abnormal state of the discharge circuit by the display circuit.
The present invention further provide a discharge current detecting circuit for a radiant heating apparatus that heats one or more workpieces by a flash emitted from at least one flash discharge lamp, a condenser, connected in series to the at least flash discharge lamp, for supplying voltage to the at least one flash discharge lamp; and a non-contact current detecting sensor provided in the discharge circuit wherein the current detecting sensor detects in a non-contact state discharge current flowing through the discharge circuit.